"There’s very little all the factories agree on, but engine rotation is one of them After sunshine, rain and fresh air, my favourite natural phenomenon is gyroscopic effect. This is because we wouldn’t be able to ride motorcycles without it. If you don’t believe me, try this next time you’re out riding: when you stop at a traffic light, don’t put your feet down. (And don’t send me the bill.) A motorcycle’s spinning wheels create gyroscopic effect that keeps the machine going straight. The more speed, the more gyro and the more stability. This is all good, unless you are racing. Most racers don’t give a hoot about straight-line stability: they’re happy to hold on like gorillas on the straights, just so long as the bike will turn left or right in the blink of an eye. And this is why all premier-class Grand Prix manufacturers – possibly for the first time in history – now run their engines backwards. It may also explain why Marc Márquez’s COTA and Argentina victories were so huge – bigger than any dry-track wins from last year. When an engine runs forward (like most streetbikes) its crankshaft rotates the same way as the wheels, thus adding to the gyro effect, which makes it more difficult to turn into a corner or change direction. The obvious way to reduce gyro effect is to reverse the direction of engine rotation, so the reverse-rotating crank reduces the total gyro effect created by the fast-spinning wheels. The beneficial effects on the dynamics of a motorcycle are significant: 2the bike will turn quicker and change direction faster; a huge consideration in modern racing when most racetracks are very tight and twisty. A reverse-rotating engine also reduces wheelies, because the crank’s torque reaction pushes the front wheel down during acceleration, rather than lifting it (although this is less important than in the days of two-strokes, when crankshaft inertia was greater.) However, nothing is for free in racing. If you run the engine backwards the engine needs an extra jackshaft to keep the rear wheel turning the right way. That shaft absorbs a significant amount of horsepower, as well as increasing engine weight and dimensions. In theory, a reverse-rotating crank also increases understeer in corners, making the bike run wide on the exit, which can prevent the rider from getting on the throttle. But presumably all these costs are worthwhile because this year Honda reversed the engine rotation of their RC213V, the first time they’ve run an engine backwards since the days of the 500s. The last time Honda went backwards was in 1987. The first NSR500, born in 1984, was a real handful, partly because its V4 two-stroke engine ran forwards. The torque reaction from the forward-rotating crankshaft lifted the front during acceleration, causing plenty of problems for riders who spent too much time fighting wheelies instead of thinking about the next corner. The NSR ran backwards from 1987 and won eight of the last 13 500cc titles."
A bit off topic and random but...
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Originally Posted by wobbly
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